EFFECT OF TIC POWDER ADDITION ON THE GRAIN REFINEMENT RESPONSE OF B319 ALUMINIUM ALLOY Vishank Kumar 1 , Lukas Bichler 1 1 UBC (University of British Columbia); Okanagan Campus; 3333 University Way; Kelowna, BC V1V 1V7, Canada Keywords: B319, TiC, thermal analysis, solute segregation, etc Abstract In this research, efficiency of grain refinement of permanent mold cast B319 aluminum alloy using titanium carbide (TiC) grain refiner was investigated. The grain refiner was added at 0.031, 0.05 and 0.1 wt%. In-situ solidification analysis was carried out, along with microsctructure and mechanical testing characterization. The results of cooling curve analysis suggest that addition of TiC delayed the time to reach the solidus temperature, increased the liquidus temperature, and decreased the amount of undercooling. Scanning Electron Microscopy (SEM) and chemical analysis revealed that Ti was present in solution uniformly throughout the matrix. Introduction Aluminum alloy B319 is a popular variant from the family of Al-7Si aluminum alloys currently used for automotive cylinder block and head components due to its optimal creep resistance, high temperature dimensional stability and corrosion resistance. B319, being a hypoeutectic alloy, solidifies by first forming a large α-Al phase, followed by second phases and eutectics. When the α-Al retains its fine and equiaxed morphology, the resulting as-cast mechanical strength, fluidity and feeding characteristics of the casting significantly improve [1]. However, in order to promote and control formation of the fine equiaxed α-Al morphology, Al-5Ti-1B master alloys are traditionally used as grain refiners. These grain refiners introduce TiAl 3 and TiB 2 substrates into the liquid metal and provide heterogeneous nucleation sites for the formation of α-Al grains [1- 3] Sigworth and Guzowski [4] have suggested that in the grain refinement of Al-Si alloys with titanium, if more than 2wt% Si is present in solution, a layer of titanium silicide forms on inoculating particles and reduces their grain refinement efficiency. A crystallographic study by Qiu [5] on the orientation relationship of nucleant sites TiAl 3 , TiB 2 with Al and Si confirmed that formation of a titanium silicide layer of Ti 5 Si 3 was the most likely cause of grain refinement poisoning. Qiu also demonstrated that TiAl 3 particles were more susceptible to the formation of the titanium silicide layer as compared to TiB 2 , because of reasonably good crystallographic interfacial matching with Ti 5 Si 3 . This approach was later expanded by experimental work where a better grain refining of Al-7Si alloys refined with boron (B) was achieved with lower amounts of titanium silicide [1,2]. However, according to duplex nucleation theory [6], TiB 2 particles alone are ineffective until covered by a layer of TiAl 3 . Recent efforts have led to the development of Al-Ti-C based grain refiners, which introduce titanium carbide (TiC) particles as heterogeneous nucleating sites. The ‘carbide’ theory postulated by Cibula [7] suggests that TiC particles directly nucleate α-Al, because of their excellent lattice matching. Extensive work [3,7- 10] supports this theory, since Ti- and C-rich crystals in grain refined aluminum grains were observed. In the work of Kumar on grain refinement of Al-7Si alloys subject to slow cooling rates [3], addition of 0.1 wt% of Al-5Ti-1.2C master alloy was seen to grain refine as efficiently as 1wt% of Al-3B or Al-Ti-3B master alloys. Kumar also reported that with higher TiC addition levels, coarser grains were observed because of agglomeration of TiC particles. This agglomeration supports previous studies of Mohanty and Gruzleski [11], which suggests that TiC particles are unstable in the Al-7Si melt and dissolve within ~30 minutes of holding time. However, at lower addition levels, TiC provides better grain refinement than Al-Ti-B or Al-B grain refiners. Yet, TiC based grain refiners, in contrast to the Al-Ti-B type, have not been established in industry as a potential grain refiners due to the difficulty in preparing Al-Ti-C master alloys. For example, formation of carbides of Al 4 C 3 and Ti 3 AlC 5 during processing of the master alloy might decrease the grain refining potency of Al- Ti-C particles [12]. Also, homogeneous introduction of Ti-C particles into the melt remains a challenge. Thus, this study focused on studying the effect of adding micron-sized TiC particles into liquid B319 aluminum alloys with the view of grain refinement. Experiment Details: Titanium Carbide (TiC) powder with a 3μm particle size was added at three addition levels to B319 aluminum alloy during permanent mold casting. Based on the work with Al-5Ti-1.2C [12], optimum addition level of TiC was expected to be at 0.031 wt%. Thus, casting trials were carried out with 0, 0.031, 0.05 and 0.1 wt% TiC addition levels. To avoid TiC agglomeration during processing, the total mass of powder was separated into four equal amounts, and individual quarters were wrapped in aluminum packets. For all casting trials, 2kg of B319 alloy were melted in an electric resistance furnace and heated to820°C, at which point Figure 1: Representative casting